1. Field of the Invention
Aspects of the present invention relate to a polybenzimidazole-base complex, a crosslinked material of polybenzoxazines formed thereof, and a fuel cell using the same.
2. Description of the Related Art
In conventional ionic conductors, ions are moved by applying a voltage thereto. Ionic conductors are widely used in electrochemical devices such as fuel cells, electrochemical sensors, and the like.
For example, in terms of generating efficiency, system efficiency, and long-term durability of components, fuel cells may use a proton conductor that can provide long-term stable proton conductivity at an operating temperature of 100 to 300° C. under non-humidified conditions or low-humidified conditions with a relative humidity of 50% or less.
The above specifications have been considered in the development of conventional solid polymer-type fuel cells. However, solid polymer-type fuel cells that include a perfluorocarbonsulfonic acid membrane as an electrolyte membrane generate insufficient energy at an operating temperature of 100 to 300° C. at a relative humidity of 50% or less.
Conventional fuel cells include fuel cells using an electrolyte membrane containing a proton conducting agent, fuel cells using a silica diffusion membrane, fuel cells using an inorganic-organic composite membrane, fuel cells using a phosphoric acid-doped graft membrane, and fuel cells using an ionic liquid composite membrane.
In addition, a solid polymer electrolyte membrane formed of polybenzimidazole (PBI) in which a strong acid, such as a phosphoric acid or the like, is doped has been disclosed (in U.S. Pat. No. 5,525,436).
The solid polymer electrolyte membrane formed of PBI described above has excellent thermal stability compared with other polymer electrolyte membranes, and thus is a suitable type of electrolyte membrane.
However, a method of preparing PBI polymer, which is well known, is a process in which PBI polymer is synthesized in a highly viscous solution under a strong acid atmosphere (Macromol. Rapid Commun. 2004, 25, 1410, J. Poly. Sci. Part A: Polym. Chem, 1989, 27, 2815). Thus, it is also well known that in each batch used in the synthesis processes, it is difficult to obtain PBI with constant physical properties.
In particular, in the above process, PBI is synthesized by a heat treatment under an acid atmosphere, and the reactants and products mainly have an amine or imine functional group, which is basic, thereby being easily protonated from the surrounding environments to have a positive charge. Therefore, it is difficult to separate pure PBI using separation methods such as general GPC, HPLC, or the like. In addition, U.S. Pat. No. 5,525,436 discloses a method of using PBI as a polymer electrolyte membrane for a fuel cell, in which the PBI is impregnated with a strong acid solution such as a concentrated phosphoric acid. However, impurities such as unreacted monomers or oligomers cannot be separated from the prepared polymer product, and thus, the impurities are allowed to remain, with disregard for their impact.
In addition, when a solid polymer electrolyte membrane prepared by doping the PBI polymer prepared using the preparation method described above with a strong acid such as a phosphoric acid is applied in a fuel cell, problems, such that characteristics of the fuel cell are not constantly obtained, mechanical strength of the fuel cell is easily degraded, or an initial activation time of the fuel cell becomes longer, frequently occur. Therefore, further improvement is desirable.